System and method for implementing a block-based backup restart

ABSTRACT

A system and method for block-based restarts are described. A data storage system interfaces with one or more nodes of a network file system on which a volume is provided in order to read data stored on the volume on a block-by-block basis. Backup data sets capable of recreating the data on the volume are generated from the data blocks read from the volume. The system can interface with a backup memory resource and write the backup data sets to the backup memory resource in a sequential order. As the backup data sets are generated and written to the backup memory resource, restart checkpoints for the data set are also regularly generated and stored for use in restarting the backup process in the event of a recoverable failure in the transfer.

RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S.application Ser. No. 14/528,340, filed on Oct. 30, 2014, now allowed,titled “SYSTEM AND METHOD FOR IMPLEMENTING A BLOCK-BASED BACKUPRESTART,” which is incorporated herein by reference.

TECHNICAL FIELD

Examples described herein relate to data storage systems, and morespecifically, to a system and method for implementing a block-basedbackup restart.

BACKGROUND

The network data management protocol (NDMP) specifies a commonarchitecture for the backup of network file servers and enables thecreation of a common agent that a centralized program can use to back updata on file servers running on different platforms. By separating thedata path from the control path, NDMP minimizes demands on networkresources and enables localized backups and disaster recovery. WithNDMP, heterogeneous network file servers can communicate directly to anetwork-attached tape device for backup or recovery operations. WithoutNDMP, administrators must remotely mount the network-attached storage(NAS) volumes on their server and back up or restore the files todirectly attached tape backup and tape library devices.

Tape devices are one conventional approach for enabling recording ofblock-based backup data. A tape device provides sequential accessstorage, unlike a disk drive, which provides random access storage. Adisk drive can move to any position on the disk in a few milliseconds,but a tape device must physically wind tape between reels to read anyone particular piece of data. In tape devices, a disadvantageous effecttermed “shoe-shining” occurs during read/write if the data transferstops or its rate falls below the minimum threshold at which the tapedrive heads were designed to transfer data to or from a continuouslyrunning tape. In this situation, the modern fast-running tape drive isunable to stop the tape instantly. Instead, the drive must decelerateand stop the tape, rewind it a short distance, restart it, position backto the point at which streaming stopped and then resume the operation.If the condition repeats, the resulting back-and-forth tape motionresembles that of shining shoes with a cloth. Shoe-shining decreases theattainable data transfer rate, drive and tape life, and tape capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example data backup system for implementing ablock-based backup restart, in accordance with some aspects.

FIG. 2 illustrates an example data storage system operable for backingup data and implementing a block-based backup restart, in accordancewith some aspects.

FIG. 3 illustrates an example sequence of operations for transferringbackup data with the capability for a block-based backup restart.

FIG. 4 illustrates an example method of backing up data in a block-basedrestart environment, in accordance with some aspects.

FIG. 5 illustrates an example method of performing a block-based backuprestart, in accordance with a first mode of operation.

FIG. 6 illustrates an example method of performing a block-based backuprestart, in accordance with a second mode of operation.

FIG. 7 is a block diagram that illustrates a computer system upon whichembodiments described herein may be implemented.

DETAILED DESCRIPTION

Examples described herein include a computer system to backup data froma network file system at the physical block level, with the capabilityto efficiently restart the backup process from a point of failure.

In an aspect, a data storage system performs operations that includeinterfacing with one or more nodes of a network file system on which avolume is provided in order to read data stored on one or more volumesof the network file system. Rather than reading file-by-file, the systemreads from the volume on a block-by-block basis. Backup data setscapable of recreating the data on the volume are generated from the datablocks read from the volume. In contrast to conventional approaches,when the backup process experiences a failure, examples such asdescribed below enable for a backup system to restart the backup readprocess from a specified block on the volume and restart the backupwrite process at a particular location in the backup resource.

In more detail, a block-based backup system is capable of interfacingwith a backup memory resource in order to write the backup data sets tothe backup memory resource in a sequential order. When a failure isexperienced by the backup system, the point of failure can be correlatedto a physical or logical location that is structured linearly inaccordance with the sequential order. In one aspect, there is only onenode and one data set backed up from the volume. In other aspects, thevolume is distributed across multiple nodes over a network and each nodegenerates its own backup data set which can be combined with the othernodes' backup data sets to recreate the data stored on the volume.

In one aspect, a backup memory resource is a tape device or tape libraryin which data is read and written to in a sequential order in accordancewith a linear physical and logical structure of the resource. In otheraspects, the backup memory resource is a cloud storage platform locatedon a remote host and the data sets are transmitted across a network inthe sequential order in accordance with a queue or other physical andlogical structure of resources for transferring data to the platformacross a network.

As the backup data sets are generated and written to the backup memoryresource, restart checkpoints for each data set are also regularlygenerated. In one aspect, these checkpoints are created after a fixedperiod of time (e.g., every 30 seconds). In other aspects, checkpointscan be created after a specified number of blocks have been read fromthe volume. These checkpoints can then be stored at a checkpointlocation such as in memory or persistent storage.

During the data backup process, the system can detect various failures,both recoverable and non-recoverable. If a failure in the backup sessionis recoverable, the system can attempt to trigger a backup restarteither with the help of a data management application or unbeknownst tothe data management application depending on the type of failure.

In one method of operation, a system interfaces with a network filesystem on which one or more nodes of a volume (or set of multiplevolumes) is provided in order to retrieve stored checkpoints for backupdata sets. In some variations, the checkpoints can be stored incheckpoint locations provided with the volumes on which the backup isperformed. Rather than generating backup data sets from the startingblock of the volume, the nodes can restart the backup session andgenerate backup data sets beginning at a block identified in the storedcheckpoint. In some aspects, when there are multiple checkpoints storedat the checkpoint location, the checkpoint referring to the earliestblock is used. In other aspects, the checkpoint referring to a blockwhich is closest to but less than a specified restart offset is used.

In another method of operation, upon detecting a failure in the backupsession requiring a backup restart, the system can signal the backupmemory resource to return to a most recent consistent position in theordered sequence prior to the failure. The system can identify a restartoffset corresponding to the most recent consistent position in theordered sequence then select a restart checkpoint based on the restartoffset. Using the restart checkpoint, the system can generate furtherbackup data sets from the read data beginning at a block identified bythe restart checkpoint and interface with the backup memory resource inorder to sequentially write the further backup data sets to the backupmemory resource.

By utilizing a block-based backup process, data can be backed up morequickly compared to a logical directory-based backup. In addition,special volume settings and configurations such as deduplication can bebacked up. However, many conventional backup restart features are notimplemented with block-based backup processes. NDMP allows data to bewritten directly to a network-attached backup device, such as a tapelibrary, but these backup devices may not be intended to hostapplications such as conventional backup software agents and clients,which can result in failures necessitating a complete restart of thebackup process. Since data backups are often very large, restarting fromthe beginning in the event of failure can be costly. In addition,writing to the same tape device repeatedly reduces its lifespan, andtransferring data over a network can be expensive in terms of bandwidthuse. Among other benefits, creating checkpoints throughout the backupsession and reading the checkpoints in the event of a failure, thebenefits of a restartable backup process can be used with block-basedbackups.

The term “block” and variants thereof in computing refer to a sequenceof bytes or bits, usually containing some whole number of records,having a maximum length known as the block size. Blocked data isnormally stored in a data buffer and read or written a whole block at atime. Blocking reduces the overhead and speeds up the handling of thedata-stream. For some devices such as magnetic tape and CKD diskdevices, blocking reduces the amount of external storage required forthe data. Blocking is almost universally employed when storing data tomagnetic tape, rotating media such as floppy disks, hard disks, opticaldiscs, and NAND flash memory. Most file systems are based on a blockdevice, which is a level of abstraction for the hardware responsible forstoring and retrieving specified blocks of data.

One or more embodiments described herein provide that methods,techniques and actions performed by a computing device are performedprogrammatically, or as a computer-implemented method. Programmaticallymeans through the use of code, or computer-executable instructions. Aprogrammatically performed step may or may not be automatic.

One or more embodiments described herein may be implemented usingprogrammatic modules or components. A programmatic module or componentmay include a program, a subroutine, a portion of a program, a softwarecomponent, or a hardware component capable of performing one or morestated tasks or functions. In addition, a module or component can existon a hardware component independently of other modules or components.Alternatively, a module or component can be a shared element or processof other modules, programs or machines.

Furthermore, one or more embodiments described herein may be implementedthrough the use of instructions that are executable by one or moreprocessors. These instructions may be carried on a computer-readablemedium. Machines shown or described with figures below provide examplesof processing resources and computer-readable mediums on whichinstructions for implementing some aspects can be carried out and/orexecuted. In particular, the numerous machines shown in some examplesinclude processor(s) and various forms of memory for holding data andinstructions. Examples of computer-readable mediums include permanentmemory storage devices, such as hard drives on personal computers orservers. Other examples of computer storage mediums include portablestorage units, such as CD or DVD units, flash or solid state memory(such as carried on many cell phones and consumer electronic devices)and magnetic memory. Computers, terminals, network enabled devices(e.g., mobile devices such as cell phones) are all examples of machinesand devices that utilize processors, memory, and instructions stored oncomputer-readable mediums. Additionally, embodiments may be implementedin the form of computer programs.

System Overview

FIG. 1 illustrates an example data backup system 100 for block-basedbackup restarts, in accordance with some aspects. The data backup system100 includes Network Data Management Protocol (NDMP) data managementapplication (DMA) 115 in communication over a network with a sourcestorage system 120 and a data backup destination 130. Data store 150,attached to source storage system 120, can be any type of physicalmemory resource such as a hard disk drive or storage area network (SAN)on which one or more volumes 155 are provided. In this context, a volumeis a single accessible storage area within a file system, accessibleusing an operating system's logical interface. In one aspect, volume 155is stored in its entirety on data store 150. In other aspects, volume155 is distributed across multiple data stores 150 and accessed by morethan one source storage system 120. In either case, when NDMP server 134running on source storage system 120 receives a DMA command 116 toperform a backup operation for volume 155, data backup engine 121retrieves data 123 from the data store 150 at the physical block level.In some aspects, data backup engine 121 sends backup data sets 125 tothe data backup destination 130. DMA commands 116 received by an NDMPserver 135 at the data backup destination 130 direct the backup datasets 125 to be written to a backup memory resource 160 (e.g., a tapedevice).

Data management application 115 communicates over a network with thesource storage system 120 and data backup destination 130. NDMP providesan open standard for network-based backup of network-attached storage(NAS) devices such as source storage system 120 and minimizes codingneeded for different applications by providing standard commands forbacking up and restoring file servers. NDMP increases the speed andefficiency of NAS data protection because data can bypass backup serversand be written directly to secondary storage at a data backupdestination 130.

NDMP addresses a problem caused by the particular nature ofnetwork-attached storage devices such as source storage system 120.These devices are not connected to networks through a central server, sothey include their own operating systems. Because NAS devices arededicated file servers, they aren't intended to host data managementapplications such as backup software agents and clients. Consequently,administrators need to mount every NAS volume by either the Network FileSystem (NFS) or Common Internet File System (CIFS) from a network serverthat does host a backup software agent. However, this cumbersome methodcauses an increase in network traffic and a resulting degradation ofperformance. Therefore, NDMP uses a common data format that is writtento and read from the drivers for the various devices, such as sourcestorage system 120 and data backup destination 130. In this manner, datamanagement application 115 can send DMA commands 116 to direct a databackup process between the source storage system 120 and the data backupdestination 130 without needing to mount volume 155 or backup memoryresource 160.

Data management application 115 communicates with the source storagesystem 120 and the data backup destination 130 to control backup,recovery, and other types of data transfer between primary and secondarystorage. In some aspects, source storage system 120 and data backupdestination 130 can be the same physical system, and data store 150 andbackup memory resource 160 can both be connected to it. In otheraspects, the source and destination are physically separated with datastore 150 connected to source storage system 120 and backup memoryresource 160 connected to data backup destination 130. Data backupdestination 130 can be a secondary storage system with its own operatingsystem and an NDMP server 135, or in another aspect, data backupdestination 130 can be a simple NDMP-compliant device.

In one example, backup memory resource 160 is a tape device, and datamanagement application 115 opens the tape device and positions itswriting mechanism to the appropriate location for backing up data. Datamanagement application 115 can establish a connection between sourcestorage system 120 and the NDMP server 135 of the data backupdestination 130. The data management application 115 can specify thevolume to be backed up (e.g., volume 155) to the data backup engine 121and trigger the backup process to begin.

During the data backup process, data backup engine 121 sends backup datasets 125 from the source storage system 120 to the data backupdestination 130. In one aspect, at programmed intervals while the backupprocess is ongoing, a checkpoint module 122 generates checkpointsrepresenting the latest block numbers read from the volume 155. In otheraspects, the checkpoints identify a virtual block number which the databackup engine 121 can use to map to a physical block number on volume155. For example, the programmed interval can be every 30 seconds. Insome aspects, checkpoints are stored with the source storage system 120itself.

In one mode of operation, in the event of a failure in the data backupprocess, the checkpoint module 122 can retrieve stored checkpoints foruse in restarting the data backup at or near the point of failure ratherthan having to restart from the beginning. In one aspect, checkpointsare saved in non-volatile memory of the data backup destination 130.Alternatively, checkpoints can be saved on physical media such as acheckpoint-file associated with volume 155 being backed up from thesource storage system. The checkpoint file can hold multiple checkpointsalong with the data offset associated with each checkpoint.

In another mode of operation, data management application 115 cancontrol the restart process in the event of failure using positioninformation 117, which may represent a mapping of positions in the databackup stream to positions in the backup memory resource 160 wherecorresponding data from the stream is written. After the failure, thedata management application 115 can reestablish a connection between thesource storage system 120 and the NDMP server 135 at data backupdestination 130. Once the connection has been reestablished, the datamanagement application 115 can signal the backup memory resource 160 toreposition itself to the last consistent position recorded, which mayrepresent the last known good write before the failure occurred. In oneaspect, this involves repositioning the writing mechanism of a magnetictape in a tape device. In other aspects, repositioning refers to asequential stream of bytes being sent over a network, for example to acloud storage system.

Once repositioned, the data management application 115 can identify adata restart offset which corresponds to the identified last consistentposition of the backup memory resource 160. This restart offset 118 anda backup context identifying the backup session can be sent to thesource storage system 120 along with a DMA command 116 to restart thebackup session.

Data backup engine 121 receives the restart backup request and looks upa checkpoint file using the restart offset 118 provided by the datamanagement application 115. In one aspect, this lookup is performed on afile on the source storage system 120 that contains a table mapping dataoffsets to checkpoints for each backup session. The data backup engine121 selects a checkpoint with an offset that is closest to but less thanthe reset offset 118 to use as a basis for restarting the backupsession.

In one aspect, checkpoints include an id, block number, progress, uniquetransfer id, and data containing checkpoint information. The idcorresponds to a common identifier for all checkpoints to be used by theoperating system and components to identify the packet as a checkpoint.Block number references the latest block number on volume 155 which hasbeen read. The block number can be a virtual block number used by databackup engine 121 to map to a physical block number on volume 155.Progress represents the state of completion of the backup process, suchas a percentage of total blocks on volume 155 that have been read andtransferred or alternatively, a number of bytes transferred. The uniquetransfer id is different for all checkpoints in the transfer andtherefore uniquely identifies each checkpoint.

A data backup system 100 may have more constituent elements thandepicted in FIG. 1, which has been simplified to highlight relevantdetails. For example, there can be multiple source storage systems 120,each with an associated backup data set 125, and the volume 155 can bedistributed among multiple data stores 150. Similarly, although FIG. 1presents data backup system 100 in the context of NDMP, data backupsystem 100 can be implemented independently of NDMP using similarprotocols.

FIG. 2 illustrates an example data storage system, in this case sourcestorage system 120 depicted in FIG. 1, operable for backing up data andimplementing block-based backup restarts, in accordance with someaspects. A source storage system 120 can include more components thandepicted in FIG. 2, which has been simplified to highlight componentsthat are used in block-based backup restarts, in accordance with someaspects.

Source storage system 120 contains an NDMP server 210 to managecommunications between data management application 115 and a data backupdestination 130 that operates to store the backup data sets 125. Thesecommunications can occur over internal LANs or external networks such asthe Internet using a variety of protocols such as TCP/IP.

In some aspects, the NDMP server 210 and an NDMP interface 215 are partof a management module in the source storage system 120 operatingsystem. The NDMP interface 215 can be a command line interface or aweb-based browser interface that allows customers, serveradministrators, or other personnel to monitor NDMP activity and issuecommands 216 to the NDMP server 210. A data module NDMP 225 controlscommunications and data flow between the NDMP server 210 in themanagement module and the other components of the data module, such asdata backup engine 121, block transfer engine 240, and backup receivelayer 245.

The data backup engine 121 is configured to accept backup commands 221from a backup engine interface 220. For example, a customer can use thebackup engine interface 220 to configure and edit configuration 221,which can include technical parameters affecting the backup process. Inone aspect, the configuration 221 can include an interval of time ornumber of blocks transferred before each checkpoint is created.

Backup Receive Layer 245 interfaces with the data backup engine 121 anddata module NDMP 225 to receive DMA commands 116. In some aspects, thebackup receive layer 245 is also connected with components that performdifferent types of backup operations, such as a dump component forlogical file-based backups. As illustrated in FIG. 2, backup receivelayer 245 can receive backup data sets 125 from data backup engine 125.In one example, backup receive layer 245 takes the backup data sets 125and sends them through a network 255 to the data backup destination 130.Alternatively, backup data sets 125 can be backed up from an attachedvolume to a physical storage medium (e.g., a tape device) directlyconnected to source storage system 120. To handle writing backup data,the backup receive layer 245 interfaces with a number of drivers andother components, such as tape driver 250 for writing to tape devices,network 255 for connection to a remote host (e.g., cloud storage or databackup destination 130), and file 260.

Block transfer engine 240 is a component for taking blocks 241 from asource volume 242 and converting them into backup data sets 125 to besent to the data backup engine 121. In one aspect, block transfer engine240 is a NetApp® SnapMirror® transfer engine. Rather than reading filesand directories from the volume, block transfer engine 240 operates atthe physical block level to read blocks 241 from source volume 242. Inone mode of operation, block transfer engine 240 identifies physicalblocks on source volume 242 through the use of virtual containersmanaged by a RAID subsystem, which provides a range of virtual blocknumbers mapping to physical block numbers.

Block transfer engine 240 replicates the contents of the entire volume,including all snapshot copies, plus all volume attributes verbatim fromsource volume 242 (primary) to a target (secondary) volume, which can beattached locally to source storage system 120 or attached to the databackup destination 130. In some aspects, block transfer engine 240 findsthe used blocks in source volume 242 and converts the changes intoReplication Operations (RepIOps) that can be packaged into backup datasets 125 and sent over the network to the data backup destination 130.In some aspects, a RepIOp represents changes to a file system in theform of messages. When replicating one volume to another, RepIOps areapplied to the backup volume at the data backup destination 130,therefore reconstructing the volume data. However, in some aspects, databackup engine 121 instead leverages the block transfer engine 240 tocreate RepIOps and package them into backup data sets 125, which aretransferred and themselves written to physical media such as a tapedevice, thus achieving physical backup. In a further aspect, backup datasets 125 represent marshaled RepIOps packaged into chunks of blockswhich can contain a header and checksum to detect corruption. Thesechunks are only written to the output stream once completely created,and the destination writes the stream to backup memory resource 160 whenreceived. In other aspects, raw data blocks from the source volume 242themselves can be sent to the data backup destination 130 and written,and these blocks can be used to reconstruct the volume data at a latertime.

In some aspects, block transfer engine 240 executes a transfer 246,writer 247, and scanner 248, whose operations are detailed in FIG. 3.Scanner 248 reads blocks 241 from the source volume 242 and sendsRepIOps and created checkpoints to writer 247, which interfaces withdata backup engine 121. In one aspect, writer 247 is executed on databackup engine 121 instead of block transfer engine 240. Writer 247additionally handles checkpoint read requests from scanner 248.

During a future data restore process, the data backup engine 121 canreconstruct the RepIOps read from the physical media and send them tothe block transfer engine 240 to reconstruct the volume. In someaspects, the data backup engine 121 only handles physical, block-basedbackups and therefore does not understand file system formats and cannotrecognize files and directories. In these aspects, data backup engine121 backs up data only at the volume level.

In one aspect, block transfer engine 240 can compress data backup sets125 to conserve network bandwidth and/or complete a transfer in ashorter amount of time. These compressed backup data sets 125 can thenbe decompressed at the data backup destination 130 before being writtento physical media, or in another aspect, the compressed backup data sets125 can be written without first being decompressed.

While reading blocks and transferring backup data sets 125, checkpointmodule 122 generates checkpoints and stores them in checkpoint store 123at programmed intervals. For example, the programmed interval can beevery 30 seconds or alternatively, a set number of blocks from sourcevolume 242. In one aspect, checkpoint store 123 is located in memory ofsource storage system 120. In another aspect, checkpoint store 123 canbe a persistent storage medium such as a hard disk. In one aspect,checkpoint module 122 is a part of the data backup engine 121. Inanother aspect, checkpoint module 122 is a part of block transfer engine240, which uses its scanner 248 to send the checkpoints to data backupengine 121.

FIG. 3 illustrates an example sequence of operation for transferringbackup data with the capability for block-based backup restarts. Whileoperations of the sequence 300 are described below as being performed byspecific components, modules or systems of the data backup system 100,it will be appreciated that these operations need not necessarily beperformed by the specific components identified, and could be performedby a variety of components and modules, potentially distributed over anumber of machines. Accordingly, references may be made to elements ofsystem 100 for the purpose of illustrating suitable components orelements for performing a step or sub step being described.Alternatively, at least certain ones of the variety of components andmodules described in system 100 can be arranged within a singlehardware, software, or firmware component. It will also be appreciatedthat some of the steps of this method may be performed in parallel or ina different order than illustrated.

With reference to an example of FIG. 3, a transfer 310 is createdthrough for example, a data backup system 100 as described with FIG. 1.In some aspects, transfer 310 can be created in response to an NMDPbackup command received from data management application 115, which canbe initiated by a user of data backup system 100 or an automatedprocess. Once the transfer 310 is created, it instantiates a scanner 320and writer 330. In some aspects, the scanner 320 is an instance of anobject executed on block transfer engine 240 as described with FIG. 2,and writer 330 is an instance of an object executed on data backupengine 121. In another aspect, writer 330 is also executed on blocktransfer engine 240. Transfer 310 can instantiate more instances ofobjects than just these two, but for the purpose of highlightingrelevant details, other objects are omitted.

Once instantiated, scanner 320 sets up the source volume for datatransfer. For example, setting up the source volume can include aquiesce operation to render the volume temporarily inactive. In someaspects, the scanner 320 sends a checkpoint read request to the writer330 at the data backup engine. Writer 330 can then translate the readrequest into a function invocation to read checkpoint information fromthe checkpoint location, which may be stored in memory at or written tocheckpoint store 123. In the case where transfer 310 is associated witha new backup process, there should not be any stored checkpointinformation for the backup. This can lead to writer 330 filling out thecheckpoint information with an empty checkpoint. However, when thebackup process has been restarted, there should be checkpointinformation for writer 330 to read. In either case, the checkpointinformation, whether empty or not is returned to the scanner 320 as partof the acknowledgement of receiving the read request.

With the checkpoint information received, the scanner 320 startsscanning the source volume from the block identified in the checkpointinformation. In some aspects, when the checkpoint was empty at thecheckpoint location, as in the case of a new backup process, the scanner320 begins at the first block of the source volume. The scanned datablocks can then be packaged as RepIOps and sent to the writer 330 for aslong as there are more data blocks on the volume that need to be backedup.

While the data blocks are being transferred, the scanner regularlycreates new checkpoints for the backup process through, for example, thecheckpoint module 122 illustrated in FIGS. 1 and 2. In one aspect,checkpoints are generated every 30 seconds. Once generated, the newcheckpoint is sent to the writer 330, which saves the checkpoint incheckpoint store 123 to use for a restart in case of a backup failure.After saving, the writer 330 acknowledges receipt of the checkpoint. Insome aspects, this process is repeated every 30 seconds until thetransfer is completed.

FIG. 4 illustrates an example method of backing up data in a block-basedrestart environment, in accordance with some aspects. The method 400 canbe implemented, for example, by data backup system 100 as describedabove with respect to FIG. 1. A block-based data backup process can beinitiated by, in one aspect, data management application 115 either froma user or automated process (410). If the process has alreadytransferred some data and is recovering from a failure, it can insteadbe restarted from a checkpoint without any effect on I/O handles or NDMPconnections.

In either case, block transfer engine 121 starts the backup process totransfer blocks of data from a source volume to storage at a backupdestination (420). As part of the backup process, an instance of atransfer object is created (422). The transfer instance can theninstantiate a scanner at the source storage system 120 which can managereading data, packaging data, and handling checkpoint creation duringthe process (424). Transfer instance also instantiates a writer whichdelivers the RepIOps/Data to the data backup engine 121, which furtherprocesses and writes to the destination through backup receive layer245, for example to tape, a file, or over a network to the data backupdestination or remote host.

In some aspects, the scanner sets up the source volume for transfer atthe source storage system 120 (430). Once the source volume is ready,the scanner sends a checkpoint read request to the writer (440). Thewriter interprets the checkpoint read request as a ReadCheckpoint( )function invocation and looks in the checkpoint location for anycheckpoints associated with the transfer. If the backup process is newor has to begin from the first block due to an unrecoverable error, thewriter should not have any checkpoint information saved associated withthe transfer (442). However, if the backup process failed due to arecoverable error, there can be checkpoint information available at thecheckpoint destination which the writer can read and return to thescanner along with an acknowledgement of receiving the read request(444).

Once the scanner receives the checkpoint information from the writer,the scanner begins reading blocks of data from the source volumestarting at the block identified in the checkpoint (450). While thetransfer is ongoing, the scanner creates checkpoints at specifiedintervals (e.g., every 30 seconds) and sends them to the writer to bedelivered to the data backup engine, which stores checkpoints incheckpoint store 123 in memory or in persistent storage.

In some aspects, a determination is made as to whether the transfer iscomplete (470). If all blocks on the source volume have beentransferred, the method 400 ends (490). Otherwise, if there are stilldata blocks remaining to be read and transferred, the method 400continues sending data and checkpoints. However, if a restartablefailure occurs during the transfer (480), the transfer can be restartedwith the same destination using the saved checkpoints as referencepoints. If there are multiple checkpoints saved at the destination, theoldest one may be used to ensure data integrity. In some aspects, thesource storage system 120 can restart the transfer without datamanagement application 115 and data backup destination 130 being madeaware of the failure. In addition, data and control NDMP connections andany I/O handles are not affected.

FIG. 5 illustrates an example method 500 of performing a block-basedbackup restart, in accordance with a first mode of operation. In thismode of operation, a backup session restart is performed after a failurewithout the failure and restart being detected by the backup manager,such as data management application 115 as illustrated in FIG. 1.

In an aspect, a data storage system performs operations that includeinterfacing with one or more nodes over a network on which a volume isprovided in order to read data stored on the volume (510). Rather thanreading file-by-file, the system reads from the volume on ablock-by-block basis. Backup data sets (e.g., RepIOps) capable ofrecreating the data on the volume are generated from the data blocksread from the volume (520).

The system can interface with a backup memory resource and write thebackup data sets to the backup memory resource in a sequential order(530). In one aspect, there is only one node and one data set backed upfrom the volume. In other aspects, the volume is distributed acrossmultiple nodes over a network and each node generates its own backupdata set which can be combined with the other nodes' backup data sets torecreate the data stored on the volume.

In one aspect, the backup memory resource is a tape device or tapelibrary in which data is read and written in a linear order. In otheraspects, the backup memory resource is a cloud storage platform locatedon a remote host and the data sets are transmitted across a network inthe sequential order.

As the backup data sets are generated and written to the backup memoryresource, restart checkpoints for each data set are also regularlygenerated (540). In one aspect, these checkpoints are created after afixed period of time such as every 30 seconds. In other aspects,checkpoints can be created after a specified number of blocks have beenread from the volume. These checkpoints can then be stored at acheckpoint location such as checkpoint store 123.

During the data backup process, the system can detect various datatransfer failures, both restartable and non-restartable. At the end ofthe failed transfer, the data backup engine 121 receives an error codefrom the block transfer engine 240 and determines whether the codeindicates a fatal, non-restartable error or not. Examples ofnon-restartable errors are errors in media and explicit aborts. Examplesof restartable errors include volume access errors, file system errors,and data marshalling errors.

If a failure in the backup session is recoverable, the system canattempt to trigger a backup restart (550). In some aspects, the backuprestart is a new transfer with the same volumes and other parametersexcept with a new transfer id. When writing backup data sets to a tapedevice, the tape may be left in its last position before the failure andresume writing where it left off. In some aspects, the backup data setsare idempotent (that is, they can be applied to the destination volumeany number of times without changing the result), and therefore multiplecopies of the same backup data set can be written to the tape devicewithout harm.

In one aspect, the system interfaces with the one or more nodes (560) onwhich the volume is provided and retrieves stored checkpoints for eachbackup data set from the checkpoint location (570). Rather thangenerating backup data sets from the starting block of the volume, thenodes can restart the backup session and generate backup data setsbeginning at a block identified in the stored checkpoint. In someaspects, when there are multiple checkpoints stored at the checkpointlocation, the checkpoint referring to the earliest block is used (580).

The system can then interface with the backup memory resource 160 againand continue writing backup data sets to the backup memory 160 resourcein a sequential order (590).

FIG. 6 illustrates an example method 600 of performing a block-basedbackup restart, in accordance with a second mode of operation. In thismode of operation, a backup session restart is performed after a failurewith the assistance of the backup session manager, such as datamanagement application 115 as illustrated in FIG. 1.

In an aspect, a data storage system performs operations that includeinterfacing with one or more nodes over a network on which a volume isprovided in order to read data stored on the volume (610). Rather thanreading file-by-file, the system reads from the volume on ablock-by-block basis. Backup data sets (e.g., RepIOps) capable ofrecreating the data on the volume are generated from the data blocksread from the volume (620).

The system can interface with a backup memory resource and write thebackup data sets to the backup memory resource in a sequential order(630). In one aspect, there is only one node and one data set backed upfrom the volume. In other aspects, the volume is distributed acrossmultiple nodes over a network and each node generates its own backupdata set which can be combined with the other nodes' backup data sets torecreate the data stored on the volume.

In one aspect, the backup memory resource is a tape device or tapelibrary in which data is read and written in a sequential order. Inother aspects, the backup memory resource is a cloud storage platformlocated on a remote host and the data sets are transmitted across anetwork in the sequential order.

As the backup data sets are generated and written to the backup memoryresource, restart checkpoints for each data set are also regularlygenerated (640). In one aspect, these checkpoints are created after afixed period of time such as every 30 seconds. In other aspects,checkpoints can be created after a specified number of blocks have beenread from the volume. These checkpoints can then be stored at acheckpoint location such as with the source storage system associatedwith the volume being backed up (645). Additionally, the data managementapplication 115 can store a mapping of positions in the data backupstream to positions in the backup memory resource 160 wherecorresponding data from the stream is written.

During the data backup process, the system can detect various datatransfer failures, both restartable and non-restartable. At the end ofthe failed transfer, the data backup engine 121 receives an error codefrom the block transfer engine 240 and determines whether the codeindicates a fatal, non-restartable error or not. Examples ofnon-restartable errors are errors in media and explicit aborts. Examplesof restartable errors in this mode of operation are network errors anddisruptions in the storage system.

If a failure in the backup session is recoverable, the system canattempt to trigger a backup restart (650). In this mode of operation, abackup session restart is performed with the assistance of the backupsession manager, such as data management application 115 as illustratedin FIG. 1. Data management application 115 reconnects to the sourcestorage system 120 and the backup memory resource 160 in order toreestablish the connection between source and destination.

Once the connection has been reestablished, the data managementapplication 115 can signal the backup memory resource 160 to repositionitself to the last consistent position recorded, which may represent thelast known good write before the failure occurred (660). In one aspect,this involves repositioning the writing mechanism of a magnetic tape ina tape device. In other aspects, repositioning refers to a sequentialstream of bytes being sent over a network, for example to a cloudstorage system.

Once repositioned, the data management application 115 can identify adata restart offset which corresponds to the identified last consistentposition of the backup memory resource 160 (670). This restart offset118 and a backup context identifying the backup session can be sent tothe source storage system 120 along with a DMA command 116 to restartthe backup session.

Data backup engine 121 receives the restart backup request and looks upa checkpoint file using the restart offset 118 provided by the datamanagement application 115. In one aspect, this lookup is performed on afile on the source storage system 120 that contains a table mapping dataoffsets to checkpoints for each backup session. The data backup engine121 selects a checkpoint with an offset that is closest to but less thanthe reset offset 118 (680).

Rather than generating backup data sets from the starting block of thevolume, the data backup engine 121 can restart the backup session andgenerate backup data sets beginning at a block identified in theselected checkpoint (685). The system can then interface with the backupmemory resource 160 again and continue writing backup data sets to thebackup memory resource 160 in a sequential order (590).

FIG. 7 is a block diagram that illustrates a computer system upon whichembodiments described herein may be implemented. For example, in thecontext of FIG. 1, data backup system 100 may be implemented using oneor more servers such as described by FIG. 7.

In an embodiment, computer system 700 includes processor 704, memory 706(including non-transitory memory), storage device 710, and communicationinterface 718. Computer system 700 includes at least one processor 704for processing information. Computer system 700 also includes the mainmemory 706, such as a random access memory (RAM) or other dynamicstorage device, for storing information and instructions to be executedby processor 704. Main memory 706 also may be used for storing temporaryvariables or other intermediate information during execution ofinstructions to be executed by processor 704. Computer system 700 mayalso include a read only memory (ROM) or other static storage device forstoring static information and instructions for processor 704. Thestorage device 710, such as a magnetic disk or optical disk, is providedfor storing information and instructions. The communication interface718 may enable the computer system 700 to communicate with one or morenetworks through use of the network link 720 and any one of a number ofwell-known transfer protocols (e.g., Hypertext Transfer Protocol(HTTP)). Examples of networks include a local area network (LAN), a widearea network (WAN), the Internet, mobile telephone networks, Plain OldTelephone Service (POTS) networks, and wireless data networks (e.g.,WiFi and WiMax networks).

Embodiments described herein are related to the use of computer system700 for implementing the techniques described herein. According to oneembodiment, those techniques are performed by computer system 700 inresponse to processor 704 executing one or more sequences of one or moreinstructions contained in main memory 706. Such instructions may be readinto main memory 706 from another machine-readable medium, such asstorage device 710. Execution of the sequences of instructions containedin main memory 706 causes processor 704 to perform the process stepsdescribed herein. In alternative embodiments, hard-wired circuitry maybe used in place of or in combination with software instructions toimplement embodiments described herein. Thus, embodiments described arenot limited to any specific combination of hardware circuitry andsoftware.

Although illustrative embodiments have been described in detail hereinwith reference to the accompanying drawings, variations to specificembodiments and details are encompassed by this disclosure. It isintended that the scope of embodiments described herein be defined byclaims and their equivalents. Furthermore, it is contemplated that aparticular feature described, either individually or as part of anembodiment, can be combined with other individually described features,or parts of other embodiments. Thus, absence of describing combinationsshould not preclude the inventor(s) from claiming rights to suchcombinations.

What is claimed is:
 1. A method comprising: generating backup data setsfrom data read from a volume for a backup session; writing the backupdata sets to a backup memory resource; generating a plurality ofcheckpoints for the backup data sets at intervals during the backupsession, wherein a checkpoint comprises an identifier of a latest blocknumber of the data; maintaining a table that maps data offsets tocheckpoints of the plurality of checkpoints; and performing a backuprestart based upon a failure in the backup session by: performing alookup to the table to identify a restart checkpoint; and restarting thebackup session to generate additional backup data sets from the databeginning at a block identified by the restart checkpoint.
 2. The methodof claim 1, wherein the performing a lookup comprises: utilizing a dataoffset to query the table for identifying a corresponding checkpoint,mapped to the data offset, as the restart checkpoint.
 3. The method ofclaim 1, wherein the performing a lookup comprises: selecting acorresponding checkpoint as the restart checkpoint based upon thecorresponding checkpoint being mapped to a data offset that is closestto but less than a reset offset used as a basis for restarting thebackup session.
 4. The method of claim 1, comprising: signaling thebackup memory resource to reposition to a last consistent positioncorresponding to a last known valid write that occurred before thefailure.
 5. The method of claim 4, comprising: identifying a restartoffset corresponding to the last consistent position of the backupmemory resource.
 6. The method of claim 5, comprising: selecting acorresponding checkpoint as the restart checkpoint based upon thecorrespond checkpoint being mapped to a data offset that is closest tobut less than the reset offset.
 7. The method of claim 1, comprising:reestablishing a connection with the backup memory resource after thefailure; and signaling the backup memory resource to return to a mostrecent consistent position in an ordered sequence of the backup datasets written to the backup memory resource prior to the failure.
 8. Themethod of claim 1, comprising: determining that the restart checkpointcomprises a restart offset closest to but less than a data offsetcorresponding to a most recent consistent position in an orderedsequence of the backup data sets written to the backup memory resource.9. The method of claim 1, wherein the volume is distributed across afirst node and a second node.
 10. The method of claim 1, wherein thegenerating backup data sets comprises: generating a first backup dataset from first data read from a first portion of the volume accessiblefrom a first node; and generating a second backup data set from seconddata read from a second portion of the volume accessible from a secondnode.
 11. The method of claim 1, wherein the generating backup data setscomprises: backing up deduplication information for the volume.
 12. Themethod of claim 1, wherein the latest block number comprises a virtualblock number mapping to a physical block number on the volume.
 13. Themethod of claim 1, wherein the checkpoint comprises a progress indicatorindicative of a state of completion of the backup session.
 14. Themethod of claim 13, wherein the progress indicator is a percentage oftotal blocks of the volume that have been transferred to the backupmemory resource.
 15. The method of claim 1, comprising: compressing thebackup data sets before writing the backup data sets to the backupmemory resource.
 16. A non-transitory machine-readable medium havingstored thereon instructions for performing a method that causes amachine to: generate backup data sets from data read from a volume for abackup session; write the backup data sets to a backup memory resource;generating a plurality of checkpoints for the backup data sets atintervals during the backup session, wherein a checkpoint comprises anidentifier of a latest block number of the data; maintain a table thatmaps data offsets to checkpoints of the plurality of checkpoints; andperform a backup restart based upon a failure in the backup session by:performing a lookup to the table to identify a restart checkpoint; andrestarting the backup session to generate additional backup data setsfrom the data beginning at a block identified by the restart checkpoint.17. A computing device comprising: a memory containing amachine-readable medium comprising instructions for performing a method;and a processor coupled to the memory, the processor configured toexecute the instructions to cause the processor to: generate backup datasets from data read from a volume for a backup session; write the backupdata sets to a backup memory resource; generating a plurality ofcheckpoints for the backup data sets at intervals during the backupsession, wherein a checkpoint comprises an identifier of a latest blocknumber of the data; maintain a table that maps data offsets tocheckpoints of the plurality of checkpoints; and perform a backuprestart based upon a failure in the backup session by: performing alookup to the table to identify a restart checkpoint; and restarting thebackup session to generate additional backup data sets from the databeginning at a block identified by the restart checkpoint.
 18. Thecomputing device of claim 17, wherein the instructions cause theprocessor to: select a corresponding checkpoint as the restartcheckpoint based upon the corresponding checkpoint being mapped to adata offset that is closest to but less than a reset offset used as abasis for restarting the backup session.
 19. The computing device ofclaim 17, wherein the instructions cause the processor to: utilize adata offset to query the table for identifying a correspondingcheckpoint, mapped to the data offset, as the restart checkpoint. 20.The computing device of claim 17, wherein the instructions cause theprocessor to: signaling the backup memory resource to reposition to alast consistent position corresponding to a last known valid write thatoccurred before the failure; identifying a restart offset correspondingto the last consistent position of the backup memory resource; andselecting the a corresponding checkpoint as the restart checkpoint basedupon the corresponding checkpoint being mapped to a data offset that isclosest to but less than the reset offset.